Recently, the performance required from copier machines or printers using electrophotography has highly increased. In general, electrophotography for copiers or printers involves a method in which a latent electrostatic image is formed on a photoconductor, subsequently the latent image is developed using the toner, the toner image is transferred onto a sheet to be fixed, for example, paper, and then the sheet is hot-pressed by means of a heat roller (heat roller fixing method). In this heat roller fixing method, improved economic situation such as in electricity consumption, increased copying speed and the like have led to a demand for a toner with good fixing property to fix the image at lower temperatures. On the other hand, in the heat roller fixing method, there is a problem of so-called the offset phenomenon in which since the surface of the heat roller is brought into contact with the toner in a molten state, the toner adheres and is transferred to the surface of the heat roller, and this adhered toner is re-transferred to a subsequent sheet to be fixed, making the sheet contaminated. The feature of not causing this offset phenomenon is one of demands for the important toner performance. Moreover, copiers and printers with higher speeds increasingly require better performance in the charging area. Thus, a toner needs much higher durability, and therefore long-term stability in plate wear is required.
Generally, there is an attempt to lower the fixing temperature by lowering the molecular weight of binding resins (binder resins), in order to make the fixing property better. However, although lowering of the molecular weight decreases the resin viscosity, it also decreases the resin strength and the cohesive power of resin at the same time, resulting in problems such as decreased toner durability and the offset phenomenon occurring about the fixing roller. In addition, there have been attempts to use as such a binding resin, a mixture of a high molecular weight resin and a low molecular weight resin, such that the mixture has a broad molecular weight distribution, or to use a binder resin with the high molecular weight portion further crosslinked. However, in these methods, the viscosity of the resin is increased, and to the contrary to the above case, it is difficult to satisfy the fixing quality.
A variety of toners have been suggested which use, instead of those styrene-acrylic resins that have been predominantly used hitherto as such binding resins required of contradictory functions, polyester resins that are rather of higher density as binder resins, (see, for example, Japanese Unexamined Patent Application Publication Nos. 61-284771 and 62-291668, Japanese Examined Patent Application Publication Nos. 7-101318, 8-3663, and U.S. Pat. No. 4,833,057); however, presently it cannot be stated that they sufficiently satisfy, in particular, the recent increasing demands of the market. Moreover, as it is being considered proper in the market to use double-sided printing and double-sided copying in view of saving resources and protecting the environment, from this point of view there is a demand on an improvement in smear resistance, in addition to the fixing property and the offset resistance.
In addition, there have been conventionally used, bisphenol A derivatives as a raw material of a toner using a polyester resin, or tin-based catalysts as the catalyst for preparation of polyester. Meanwhile, there is a recent demand in the market from the perspective of environmental protection, on products that do not contain bisphenol A, tin or the like, as there is an opinion that these substances may have adverse effects on the environment in various ways.
Furthermore, from another perspective of saving resources, owing to the exhaustion of resources associated with recent increase in population and extension in energy consumption, saving of resources and energy as well as recycling of resources are highly desired. PET bottles, inter alia, that are collected from local communities are increasingly used in textiles or containers, and there is also a demand for further development of new applications.